It looks like it could be optional, but it would be like selling a Wii without a Wiimote. You will miss the experience if you never use the gamepad, but I suppose the question to be asked is, what is the Wii U experience, and how does the gamepad add to it, or deter from it?

I think that the gamepad should not be optional because that would take away some of the uniqueness of the system. However I am quite disappointed when I see games such as Donkey Kong Country Tropical Freeze, a great game but it doesn't use the gamepad for anything but off TV play.